The acclaimed scribe said that the two comics will offer "extremely different viewpoints" with one focusing on iconic characters and the other exploring unrealised potential.
"It's all about exploring the potential of heroes who are underrated or undervalued and not quite perceived as the A-list. And it's about Steve Trevor's determination to turn them into that," he told CBR.
The Justice League of America roster includes Catwoman, Vibe, Hawkman, Katana and the new Green Lantern Corps recruit, characters Johns is planning to develop over the course of the series.
"Vibe gets called out a lot because he's a very unlikely character. And that's fine. We've also got the new Green Lantern and Hawkman and Katana," he added.
"Where are these characters going to go? We know that at the end of the day, Superman, Batman and Wonder Woman are going to be around. But... we don't know what direction these guys will take.
"Are they going to make it on the team? What will they evolve into - or devolve into in the case of one of them? So JLA is really becoming its own beast - a different thematic world of the B and C-List whereas Justice League is strictly A."
Illustrated by David Finch, Justice League of America #1 arrives in stores on February 6.